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The European Space Agency is beginning preparations for another collaboration with NASA, this time for a mission to Europa, the icy moon of Jupiter.

Officials on both sides of the Atlantic are keen to renew the partnership that made the Cassini-Huygens mission such a success, BBC Online reports. A joint working team has been established to look into the role each agency might play, the possible spacecraft involved, and what the mission objectives would be.

Europa is an icy ball, slightly smaller than Earth's moon. Scientists suspect that the tidal forces it is subjected to because it is so close to Jupiter could generate enough heat to sustain liquid water below the surface. The tides certainly create plenty of cracks on the moon's surface, and the fact that many of these are tinted reddish-brown has prompted speculation that there could be microscopic life below the ice. It is this possibility which really makes Europa an irresistible target.

Professor David Southwood, director of science at ESA, says that he piqued the interest of the Americans during meetings held last week. But both parties have an interest in working together rather than going it alone.

NASA was planning to send a mission to Jupiter's moons, but funding has since been re-allocated to support Bush's goal of sending a manned mission to our own moon, and the Jupiter Icy Moons Orbiter (Jimo) mission has been shelved for the time being. Europe, meanwhile, has no expertise in radioisotope thermal generators, the preferred power system for such missions.

"I'd much rather do this with RTGs," Professor Southwood told the BBC News site. "And that makes it almost certainly a joint venture with the Americans and why should we do it separately?"

Another area for consideration is how to look below the ice. On one hand, deep penetrating radar scans from orbit are likely to provide a great deal of information, but Professor John Zarnecki, head of the surface science package on the Cassini-Hygens mission to Titan, says that the pressure to go to the surface will be immense.

This poses a huge challenge for mission designers, who will have to figure out a way of drilling or melting through as much as 30km of ice to get to the liquid beneath.

"If it is technically feasible to go to the surface, you would want to do that. Huygens' surface image on Titan says everything," Zarnecki told the BBC. "But, it may be that what you want to do - to look below Europa's ice - you can do that better from orbit."

Either way, the mission is in the very early planning stages: the earliest any craft will get underway is 2016. ®